An augmentor of a gas turbine engine forms an additional combustion chamber for afterburning in the gas turbine exhaust. Extremely high gas temperatures exist which would severely damage the gas flow confining duct.
It is therefore known to provide thermal liners within the augmentor duct to protect the duct from these excessive temperatures. The liner itself must be cooled and accordingly cooling air is supplied between the liner and duct for convection cooling of the liner, and also for passing a portion of the air through perforations in the liner to provide additional cooling.
The material of these liners is very thin, on the order of 0.6 millimeters, to minimize weight and avoid stresses during thermal transients. Despite the cooling, these liners operate at high temperature.
The cooling air supplied externally of these liners is at a higher pressure than the gas within the liner and accordingly, an external pressure is exerted on this liner. This creates a tendency for the liner to collapse or buckle under the external loading.
Since the liner may operate on the order of 600 degrees C hotter than the surrounding duct it expands realtive thereto. Any restraint imposed on this expansion also causes a buckling tendency in the liner. When operating at high temperature, the creep strength of the material drops off and there is a tendency for the liner to sag over time.
It is known to support the liner from axial movement at the upstream end and to guide the liner at the downstream, thereby permitting longitudinal expansion of the liner with respect to the surrounding duct. Rings have been located in the cooling air stream around the liner to provide support from buckling. These rings have been secured to the liner with a truss-like arrangement. During expansion of the liner the strain is locked in the liner by the external restraint, with this sometimes leading to local buckling and possible tearing of the liner.